Platinum is a precious metal and is relatively expensive. In recent years platinum has come into increasing prominence as a metal used for jewelry fabrication. Platinum for fine jewelry is commonly sold in high concentrations of over 85 percent by weight.
Pure platinum metal (Pt1000) is soft and does not have the mechanical strength for most jewelry applications. For this reason, in most jewelry applications various kinds of platinum alloys are employed. Platinum alloys are desirable for their neutral color when combined with gems, they are hypo-allergenic, they have high tensile strength, and a pleasurable heft due to their high-density.
The jewelry industry uses three main classes of platinum alloys. These classes are Pt950, Pt900 and Pt850. These alloys have a platinum content of 95, 90 and 85 wt. %, respectively. Commercially available alloys frequently used in the fabrication of jewelry include Pt/Ir 900/100 (90 wt. % platinum and 10 wt. % iridium), PtCu950 (95 wt. % of platinum and 5 wt. % of copper) and PtCo950 (95 wt. % of platinum and 5 wt. % of cobalt).
Various high platinum content jewelry materials are known in the art. The term “high platinum content” as used herein refers to platinum alloys having a platinum content equal or greater than 85 wt. %.
For example, U.S. Pat. No. 4,165,983 describes an alloy for fabricating jewelry containing at least 95 wt. % platinum, 1.5 to 3.5 wt. % gallium, and a balance of at least one of indium, gold, palladium, silver, copper, cobalt, nickel, ruthenium, iridium and rhodium. U.S. Pat. No. 5,846,352 describes a heat-treated platinum-gallium alloy for fabricating jewelry containing 1 to 9 wt. % gallium and a small amount of palladium. Japanese published patent application JP 61-133340 describes an alloy for fabricating jewelry consisting of 84 to 96 wt. % platinum, 1 to 10 wt. % gallium, 0.5 to 10 wt. % copper, and 0.01 to 5 wt. % cobalt. Japanese published patent application JP 61-034133 describes an alloy for fabricating jewelry containing 84 to 96 wt. % platinum, 0.5 to 10 wt. % cobalt, 0.5 to 10 wt. % copper and 0.01 to 0.5 Y, B, CaB mischmetal.
Although such alloys have satisfactory mechanical and optical properties that make them suitable for jewelry fabrication, these alloys are expensive to produce due to their high platinum content.
There are also a number of low platinum content jewelry materials known in the art. The term “low platinum content” as used herein refers to platinum alloys having a platinum content smaller than 85 wt. %.
U.S. Pat. No. 6,048,492 describes a platinum alloy composition for use in jewelry products containing about 58.5 wt. % of platinum, 26.5 to 36.5 wt. % of palladium and 5 to 15 wt. % of either iridium, copper or ruthenium. U.S. Pat. No. 2,279,763 describes a ductile platinum alloy containing 10 to 80 wt. % of platinum, 12 to 90 wt. % of palladium, and 1 to 15 wt. % of ruthenium.
A disadvantage of known low platinum content jewelry materials is that they often have inferior mechanical and physical properties compared to the high platinum content jewelry materials. In particular, the castability of known low platinum content jewelry materials is not as good as that of high platinum content alloys. Also, the color of known low platinum content jewelry materials differs from the typical “platinum color” of Pt950 alloys that is desired by most customers of fine jewelry. Hence, low platinum content jewelry materials are often rejected by customers for aesthetical reasons. In fact, it is very difficult to produce a low platinum content jewelry material that combines both the mechanical strength and workability as well as the optical properties of high platinum content materials.
Due to the potential improvements in properties and performance of such alloys, there is a need for additional alloys suitable for use in jewelry and art applications.
Another disadvantage of known low platinum content jewelry materials is that they generally comprise alloys of platinum and at least one other precious material such as palladium and/or ruthenium, which are themselves relatively expensive materials, so that jewelry made from known low platinum content materials is still relatively costly.
Accordingly, it would be desirable to provide a platinum alloy composition suitable for jewelry that is less expensive than the platinum that is presently available, yet still provides a platinum jewelry item with desirable technological and optical properties.
It would also be desirable to provide low platinum content alloys consisting essentially of platinum and non-precious metals in which the platinum content comprises 58.5 wt. % or 75 wt. % to correspond with 14 karat or 18 karat on a 24 karat scale in order to facilitate an understanding in the minds of consumers (who are familiar with the karat scale from its use in connection with gold alloys) of the weight percentage of platinum contained in the alloys.